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机载SAR图像的动态金字塔实时显示技术

项海兵,刘劲松,吴涛,赵洪立,孙龙(中国电子科技集团公司第三十八研究所孔径阵列与空间探测安徽省重点实验室, 合肥 230088;河北师范大学数学与信息科学学院, 石家庄 050024)

摘 要
目的 随着机载SAR(合成孔径雷达)图像分辨率越来越高,幅宽越来越大,传统雷达显控系统将整幅图像放入内存、抽样显示的现有方法存在内存资源紧张、显示图像的等待时间过长等问题,为解决此类问题,提出一种动态金字塔实时显示技术。方法 机载SAR图像实时显示软件包括动态金字塔构建和显示技术。动态金字塔构建技术包括:当接收到一个瓦片的图像数据时,输出第0层级的金字塔瓦片;分6种情况,生成高层级瓦片,随着接收数据不断增多,逐步补全金字塔文件。动态金字塔显示技术是指在瓦片数据不全的情况下,采用递归算法,读取较低层级瓦片,合成、显示当前显示层级图像的技术。这两种技术分属两个独立线程,以硬盘文件(瓦片)为接口,实时交互,协同工作。结果 机载SAR图像实时显示软件仅仅占用30 MB内存,且与图像大小无关;显示第1块SAR图像瓦片的时延小于1 s,与传统显控系统对比,减少约一帧图像的传输时延;显示整帧图像的时延因存储介质读写文件的速率存在差异较大,固态硬盘的时延比较稳定,显示1 GB图像的时延为12.55 s;机械盘的时延受读写速度的影响,当发送时间间隔大于6 ms时,显示1 GB图像的时延仅比传输时延多1.47 s。结论 机载SAR图像实时显示软件能实时向用户呈现接收中的SAR图像,提高了机载SAR图像的显示时效性,降低了机载雷达显控终端的内存需求,改善了机载雷达显控终端的用户体验。
关键词
Real-time display technology of airborne SAR image in pyramid format

Xiang Haibing,Liu Jinsong,Wu Tao,Zhao Hongli,Sun Long(Key Laboratory of Aperture Array and Space Application No. 38 Research Institute of CETC, Hefei 230088, China;College of Mathematics and Information Sciences, Hebei Normal University, Shijiazhuang 050024, China)

Abstract
Objective With the increasing resolution of airborne SAR (synthetic aperture radar) images and large swath width, the conventional radar display and control system directly store the entire image in memory for sampling and displaying. The problems of conventional methods are resource-intensive and time-consuming, among others. The image pyramid method can effectively allocate and use memory when displaying large images. Previous studies required an entire image as input for display, which cannot meet the requirement of real-time display in application. Develop real-time display software for airborne SAR images with little memory consumption and independent of image size. When the received image size is larger than one tile, the image will be displayed to the user in real time, and will zoom to the original resolution. Methods The real-time display techniques proposed in this study include dynamic pyramid construction and display techniques. The processes of dynamic pyramid construction in detail are as follows:outputting the 0th-level pyramid tiles when receiving tile data; then, six cases are used to generate higher-level tiles. With the increasing numbers of received data, the pyramid file is gradually completed. The dynamic pyramid display technology uses a recursive algorithm to read low-level tiles and synthesizes and displays the current display hierarchy images when the tile data is incomplete. These two technologies run in two threads, interact with hard disk files (tiles) as interfaces, and work together. Result In the real-time display software, we add a separate thread to read 64 MB (8 192×8 192 pixels), 256 MB (16 384×16 384 pixels), and 1 GB (32 768×32 768 pixels) test image files and send a data block of 256×256 pixels to the pyramid module. The time intervals for data transfer vary from 10 ms to 1 ms. The display software runs on solid state hard (SSD) and mechanical disks. The time delay of displaying the first tile and the complete frame of the image is counted. the SAR image real-time display software occupies only 30 MB of memory and is independent of image size. The results show that the use of the SAR image real-time display technology results in a time delay of less than 1 s for displaying the first SAR image tile. Compared with the traditional display control system, the transmission delay of one frame image can be reduced. The delay of an entire frame image display varies greatly due to the access rate of the storage media. The time delay of SSDs is relatively stable, which is related to the size of the image. The larger the image, the greater the delay and the larger the difference between the delay and transmission delay (delay difference). The display delay differences for 64 MB, 256 MB, and 1 GB images are 0.76 s, 3.06 s, and 12.55 s, respectively. The delay of the mechanical disk is divided into two cases:at a sending interval of less than 6 ms, the time delay is relatively stable due to the limitation of hard disks' read/write speed, which is the time required to construct the pyramid for the entire image. The building pyramid time of the 64 MB, 256 MB and 1 GB images is approximately 5.779 s, 23.55 s, and 104.202 s, respectively. At the time interval of more than 6 ms for sending images, the time delay of displaying a frame of image is increased and accompanied by a decrease in transmission rate. Thus, the size of the delay is positively correlated with the size of the image. The delay differences for the 64 MB, 256 MB, and 1 GB images are approximately 0.01 s, 0.15 s, and 1.47 s, respectively. Conclusion The technique developed in this study can present received SAR images to users in real time, improve the display time effectiveness of airborne SAR images, reduce the memory requirements of the airborne radar display and control terminals, and improve user experience in terms of airborne radar display and control terminals.
Keywords
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